1. Field of the Invention
The present invention relates to a passive RFID (Radio Frequency Identification) system and, more particularly, to a passive RFID system and method capable of recognizing a great deal of tags at a high speed by using a slot-based multi-subchannel access scheme.
2. Description of the Related Art
In general, an RFID is a technique of reading or writing information in a non-contact manner from a tag having unique identification information by using a radio frequency, in order to recognize, track and manage a tagged article, an animal, a person, and so on.
An RFID system includes a plurality of tags (e.g., electronic tags or transponders) having unique identification information and attached to articles, animals, and so on, and an RFID reader (or interrogator) for reading or writing tag information.
The RFID system is divided into a mutual induction type RFID system and an electronic wave type RFID system depending on a mutual communication scheme between a reader and a tag, divided into an active RFID system and a passive RFID system depending on whether or not a tag is operated by power of the system itself, and divided into a long-wave RFID system, a medium-wave RFID system, a short-wave RFID system, an ultrashort-wave RFID system, and a ultrahigh frequency RFID system depending on the utilized frequency.
In particular, an RFID application fields are gradually extending from the current pellet and box-unit recognition to an individual unit article recognition, and an RFID of the individual unit article application requires techniques for recognizing a great deal of articles at a high speed.
The existing class 1 Gen2 standard of the UHF band retains a technique of simultaneously recognizing a great deal of tags by using a Q random collision prevention algorithm; however, because a plurality of queries and response packets are configured as a round in which communication is performed between a reader and a tag, as the number of tags within a reader recognition range, time required for the reader to recognize the entire tags is sharply lengthened.
To overcome this problem, the TOTAL (Tag Only Talks After Listening) scheme of the “wireless communication system” of US 20090045923 employs an ALOHA algorithm in which a tag first queries and then, when the tag receives energy from a reader, the tag immediately transmits its ID to the reader, unlike the existing RFID standard. This technique is advantageous for fast and instantaneous recognition between the reader and the tag.
However, as there is no query command for the reader to control the tag, this technique is only suitable for the recognition of a few tags. That is, in the ALOHA algorithm according to which each tag randomly selects a packet transmission start time to transfer data, if the number of tags increases, inter-tag packet collision increases, so the reader fails to recognize a greater deal of tags.
Meanwhile, an international standardization of an ISO 18000-3 mode 3 (HF Gen2) protocol is ongoing in order to apply the UHF band high performance Gen2 protocol standard to an HF band favorable to a metal and liquid environment.
The ISO 18000-3 mode 3 protocol standard includes a mandatory 18000-6C UHF Gen2 protocol-based transmission scheme and an optional 18000-3 mode 2-based air interface. The 18000-3 mode 2 protocol standard of HF band RFID minimizes a transmission interference between a reader and a tag by using a phase jitter modulation (PJM) scheme and adopts a frequency multi-division scheme for simultaneously receiving a plurality of tags by using multiple channels, thus exhibiting good performance compared with the existing HF band protocol like 14443 A/B or 15693. Also, the standardization of the 18000-3 mode 3 protocol standard is ongoing, so as to adopt the PJM scheme of the characteristics of the 18000-3 mode 2 as an option by interworking with the Gen2 protocol.